On offshore platforms or vessels, drilling rigs, aircraft, HVDC systems, wind power grids, or similar DC systems, much equipment is deemed to be critical and regulatory requirements specify the availability of power in the event of a fault. Consequentially, it has been normal practice to separate the equipment on the vessel, or rig, into sections and provide separate power to each section, with redundancy, so that if a fault occurs in one section, it does not transfer to the other and not all operational capability is lost. This separation has been achieved by operating with bus ties between the sections normally open and only in limited circumstances closing those bus ties to enable one side to receive power from the other. However, such bus ties are only available for low voltage DC systems. For high voltage systems, mechanical breakers must be used.